The present invention relates to a microfilm reader and in particular to an X-ray microfilm reader having diagnostic quality resolution for the reading of X-rays.
Many types of microfilm readers are known in the prior art as evidenced by the apparatus disclosed in U.S. Pat. Nos. 3,655,279, 3,836,242, 3,871,759, 3,961,846, 4,025,177 and 4,067,648.
The basic difference between an X-ray microfilm reader and other readers whose prime function is to display various forms of data or design committed to paper and microfilm, is that the paper readers are built to design objectives which are considerably different from those of a good X-ray reader. This is true primarily for the reason that the original document medium presents a totally different technical consideration for minification and faithful blowback and for the reason that the user needs in the case of paper are satisfied by simple legibility of the data presented. For X-rays, the need is far more sophisticated, since if the image is to have diagnostic value, its presentation must enhance characteristics subject to interpretation. The quality of the image depends on high resolution of detail which is not required for paper readers and controls by which the operator-viewer may vary the degree and placement of light and/or masking off of distracting areas, requirements which are not normally present in paper data microfilm readers. Even the exact dimensions of the microfilmed image, are critically important for an X-ray microfilm reader since radiologists must often diagnose changes in a patient's condition by comparing measurements to prior examinations. To be of value in this respect, the blowback image must be a precise dimensional duplicate of the original X-ray. There is no equivalent requirement for this in a paper microfilm reader.